Very little is known about cytokinin structure and regulation in lower plants, limiting our ability to study cytokinins in relation to green plant evolution. Previous research suggested that green algae, mosses, ferns and horsetails contain isopentenyl adenine, zeatin and the riboside and ribotide conjugates; gymnosperms and angiosperms contained a more complex group of cytokinins, including dihydrozeatin (DHZ), N-glucoside and O-glucoside conjugates (Auer, 1997, Pl Growth Regul 23:17-32). We are examining the endogenous cytokinins in five lower plants in the Bryophyta and Tracheophyta: Pallavicinia lyellii (liverwort), Funaria hygrometrica (moss), Sphagnum angustifolium (moss), Selaginella kraussiana (club moss) and Nephrolepis exaltata (fern). Tissue cultured plants were used to reduce possible cytokinin contamination from microorganisms. Cytokinin analysis consisted of: extraction, addition of [3H] cytokinin tracers, 3 column chromatography steps, HPLC and analysis by capillary-LC-frit-FAB MS. In Nephrolepis fern sporophyte tissue, isopentenyl adenosine, zeatin riboside and zeatin-O-glucoside were identified; no DHZ or N-glucoside conjugates could be detected. This is the first report of an O-glucoside conjugate in any lower plant. Preliminary experiments showed that fern tissue exposed to [3H] benzyladenine (BA) for 6 hours was unable to produce detectable amounts of BA conjugates, in contrast to Arabidopsis which rapidly produced BA riboside, ribotide and N-glucoside conjugates in the same conditions. Information will be provided on the developmental response of fern rhizome tips to BA and the patterns of cytokinin structure and metabolism in these lower plant species relative to plant evolution.

Key words: cytokinin Bryophyta Tracheophyta